In furnaces of supercritical variable-pressure once-through boilers in the related art, particularly, vertical-tube furnaces having furnace walls formed of multiple boiler evaporation tubes arrayed in the vertical direction, it is important to adjust the flow rate of an internal fluid flowing in the furnace walls.
Specifically, with regard to the flow-rate adjustment of the internal fluid flowing in the furnace walls (front wall, rear wall, and left and right walls), appropriate flow-rate distribution from a partial load to a rated load is necessary in accordance with the amount of heat absorbed by the respective wall surfaces. Therefore, in the boiler structure of the related art, orifices are provided at the furnace inlets for adjusting the flow rate of the internal fluid described above.
In a boiler device of the related art, a technology for performing distributive adjustment of the feedwater flow rate between the furnace walls or between divided blocks is known. In this technology of the related art, flow-rate control valves are provided at the inlets of the furnace walls, and the fluid temperature detected at the outlets of the furnace walls is input to a control device. Therefore, the control device automatically controls the feedwater flow rate and performs distributive adjustment by controlling the degree of opening of the flow-rate control valves so that the input fluid temperature at the outlets becomes equal to a target value (for example, see Patent Literatures 1 and 2).